Simultaneous fractionation of multiple classes of polyphenols from honeybush tea using solid-phase extraction

The structural diversity of polyphenols and the inherent limitations of current extraction techniques pose a challenge to extract polyphenols using a simple and green method. Hence, in this study, a method was developed to simultaneously fractionate multiple classes of polyphenols by only varying ethanol-water solutions. Honeybush tea, which is rich in polyphenols, was selected as a model for this study. Solvent extraction followed by solid-phase extraction (SPE) was developed to obtain a polyphenol-rich fraction from six honeybush samples. Based on a gradient elution programme (10%, 30%, 50%, 70% and 90% (v/v) ethanol-water solution) of SPE, the Strata X cartridge showed a better recovery of most targeted polyphenols under 0.9 mL of the drying volume and 1 mL min⁻¹ of the dispensing speed. The elution programme for fractionating most polyphenols was as follows: single elution with 50% ethanol, followed by twice elution with 70% ethanol. The antioxidant capacity was used to analyse the differences among the polyphenol-rich fractions from six honeybush samples. Principal component analysis (PCA) revealed that unfermented C. genistoides (GG) has the greatest antioxidant capacity among the honeybush species studied. Additionally, mangiferin, isomangiferin and vicenin-2 were the main contributors to the antioxidant capacity in six honeybush fractions according to the correlation study.     

Analysis of trace mercury in water by solid phase extraction using dithizone modified nanometer titanium dioxide and cold vapor atomic absorption spectrometry

A new method for analysis of trace mercury in water samples was developed, based on the combination of preconcentration/separation using dithizone-modified nanometer titanium dioxide (TiO2) as a solid phase extractant and determination by cold vapor atomic adsorption spectrometry (CVAAS). Dithizone was dissolved with alcohol and loaded on the surface of nano-sized TiO2 powders by stirring. The static adsorption behavior of Hg2 on the dithizone-modified nanoparticles was investigated in detail. It was found that excellent adsorption ratio for Hg2 could be obtained in the pH range of 7-8 with an oscillation time of 15 min, and a 5 mL of 3.5 mol·L-1 HCl solution could quantitatively elute Hg2 from nanometer TiO2 powder. Common coexisting ions caused no obvious influence on the determination of mercury. The mechanisms for the adsorption and desorption were discussed. The detection limit (3σ) for Hg2 was calculated to be 5 ng·L-1. The proposed method was applied to the determination of Hg2 in a mineral water sample and a Zhujiang River water sample. By the standard addition method, the average recoveries were found to be 94.4%-108.3% with RSD (n = 5) of 2.9%-3.5%.     

Analysis of lipid classes by solid-phase extraction and high-performance size-exclusion chromatography

An improved method to analyze lipid classes of edible oils and fats by solid-phase extraction (SPE) and high-performance size-exclusion chromatography (HPSEC) is presented. A mixture of lipid standards was fractionated by the solid-phase extraction procedure (NH₂ phase) into polar and nonpolar fractions; these were then submitted to analysis by HPSEC. The size-exclusion chromatographic columns were three styrene/divinylbenzene columns with pore sizes of 100 Å and 50 Å. Light-scattering was used for the detection system, and the parameters of the detector were optimized to minimize the difference between the responses of the compounds studied. With this procedure it was possible to separate the following lipid classes: triacylglycerols, diacylglycerols, monoacylglycerols and free fatty acids, sterols, sterol esters, tocopherols and carotenoids. Quantitative analysis was studied for a light-scattering detector with several lipid standards of different molecular weights and unsaturation levels.     

130t RH脱碳模型建立及超低碳钢处理工艺优化

建立了RH真空处理脱碳数学模型，并通过130t RH工业试验结果对此数学模型加以验证。根据模型分析了[C]0、[O]0、真空度、提升气体流量等对脱碳效果的影响，据此优化了处理工艺，取得较好的效果。     

Evaluation of oxidative stability of canola oils by headspace analysis

Lipid oxidation is a major factor affecting flavor quality and shelf life of vegetable oils. Oxidative stability is therefore an important criterion by which oils are judged for usefulness in various food applications. In this study a method based on headspace analysis was developed to evaluate relative oxidative stability of canola oils. The method does not require the use of chemicals, involves minimal sample preparation, and can be performed on a relatively small sample size in comparison with traditional wet chemical methods. Canola oils freshly extracted in the laboratory from different seed samples were subjected to accelerated oxidation and analyzed for PV by standard methods and headspace volatiles by solid phase microextraction/GC-MS. Forward stepwise regression analysis of the data revealed a relationship between PV and headspace concentration of the volatile lipid oxidation products hexanal and trans,trans-2,4-heptadienal. The PV calculated using this formula correlated (R ²=0.73) with those measured by conventional methods. Presented in part at the 96th Annual Meeting of the AOCS, 1–4 May 2005, Salt Lake City, UT.     

固相萃取净化-气相色谱-质谱法测定染料中7种指示性多氯联苯

本文建立了以固相萃取(SPE)前处理净化、结合气相色谱-质谱(GC-MS)测定染料中7种指示性多氯联苯的分析方法。该法将染料样品经溶剂萃取后,通过固相萃取(SPE)净化、浓缩,气相色谱-质谱采用选择离子监测模式(SIM)测定,以保留时间和特征离子定性,外标法定量。     

固相萃取技术在农药残留分析中的应用

固相萃取是一种新型的样品预处理技术，操作简便，节省有机溶剂，易于实现自动化操作，已广泛应用于环境保护、药物检测、食品检验检疫等领域。在农药残留分析中，固相萃取技术的应用还使得提取不同类别农药的选择性增强，样品回收率提高，尤其是结合HPLC—MS、GC-MS、CE-MS等仪器的联合鉴定，可实现自动化分析，能简单、快速、灵敏地提取定量许多物质，从而大大提高了分析效率和精密度，具有广阔的发展前景。     

多次顶空固相微萃取方法的原理及应用

详细讨论了多次顶空固相微萃取(MHS-SPME)技术的原理和影响因素,并与常用的固相微萃取(SPME)定量校正方法相比较,分析了该方法的优势和缺点。综述了多次顶空固相微萃取在食品、农业领域的应用情况,并对该方法存在的问题和发展前景进行了论述。     

NHD脱碳工段技改总结

合成氨装置脱碳工段采用NHD脱碳工艺,由于脱碳后的脱碳气中CO2含量偏高,造成H 2损耗较大,为此采用ZUPAC系列双向金属折峰式波纹填料和新型槽盘式液体分布器对脱碳塔进行改造。改造后,脱碳气中CO2体积分数从2.0%降至1.6%,年可增加经济效益1000万元左右。     

合成氨装置中高温氢腐蚀问题探讨

探讨合成氨装置中的高温氢腐蚀问题,结合实际说明高温氢腐蚀的影响因素,提出预防高温氢腐蚀的措施.